The characteristics of semiconductor components, such as the threshold voltage of a transistor, will tend to vary with temperature. To maintain operation of circuits such as oscillators within a desired frequency range over an expected operating temperature range will therefore generally require some kind of temperature compensation. In conventional oscillators this may be achieved for example by stacking (i.e. placing in series) components having opposing temperature dependent threshold voltages, with one affecting the oscillation frequency proportional to absolute temperature (PTAT) and the other affecting the frequency complementary to absolute temperature (CTAT). Doing so, however, inevitably results in a minimum supply voltage of two threshold voltages plus any overhead of one or two overdrive voltages being necessary. In applications where a sufficient voltage is available this may not be a problem. However, in applications where a voltage supply is limited, for example in RFID tags, this can result in the oscillator requiring more power than is available or limiting the range of operation.